The invention relates in general to an analyzing of operational conditions of an internal combustion engine, and in particular it relates to a method of and a device for analyzing the series of output signals from a sensor installed in an internal combustion engine for picking up data characteristic of operational conditions of the engine. The sensor is of the type which delivers a succession of electrical signals whose waveform is dependent on the measured value.
An important characteristic value for determining operational state of an engine or for controlling or regulating an optimum operation of the latter is the dosed amount of fuel. Especially in the case of gas engines having a direct injection of fuel there is the possibility to determine the dosed amount of fuel at known pressure in its supply conduit by measuring the time of opening of the fuel injection valves. A particular method for determining the duration of injection is based on the detection by means of a sensor of the stroke or velocity of the nozzle needle in the injection valve.
For example, in the German publication No. 3,032,381 an electronic control device is disclosed in which a signal corresponding to the duration of injection is employed for controlling or regulating various magnitudes such as the start of injection, the amount of injection or the rate of exhaust gas return. In this known device, a nozzle needle sensor is used as a pickup of the measured values, whereby the electrical output signals are generated in response to the movement of the nozzle needle of the injection valve in an inductive element. According to FIG. 4 of the aforementioned German publication, the inductive element is energized from a source of constant current. In analyzing the output signals, the latter are subjected to a single or repeated differentiation to increase the steepness of the flanks of the wave forms and then the signals are fed through threshold switches.
The disadvantage of this prior art arrangement is the fact that due to the dependency of the output voltage of the sensors of the movement of the nozzle needle on the rotary speed of the engine, considerable errors may occur under circumstances in the determination of the beginning and of the end of the fuel injecting process. In addition, high frequency interference signals in pulses of a relatively large amplitude are superposed to the measuring signals of the needle stroke sensor. These interference signals result from changes of movement of the nozzle needle which in practice are truly complicated during the closing and opening of the fuel injection valve. Different output voltages may be caused also due to variations of electrical output data occurring from one sensor to another and consequently the threshold levels of the threshold switches must be adjusted individually.